The ultimate aim of the proposed research is to understand the nature of the processes underlying perceptual organization which has been recognized, since the work of the gestalt psychologists, as basic to all perception. On the assumption that the grouping of visual input is a multilevel process, experiments are proposed which are designed to isolate what kinds of organization occur at what levels in the visual system. We will also examine whether the groupings that occur at different levels entail attention. We expect to find that the lower the level of the grouping process, the less likely is attention to be factor. The measures of perceived grouping will include subjects' reports of apparent grouping, reaction times to detect grouping and ratings of segregation strengths. Because the questions these experiments address have not yet received adequate answers and because they concern such a fundamental aspect of all perception, the research proposed is likely to have important ramifications for both normal and abnormal functioning.